1. Field of the Invention
The present invention relates to a circuit for lighting a discharge lamp and, in particular, refers to an electronic ballast circuit for fluorescent lamps.
2. Description of the Related Art
Discharge lamps (for example, fluorescent lamps) provide light in numerous commercial, industrial, and consumer applications. The discharge lamps are illuminated when driven by an alternating current (AC) signal, such as signals from a power line which oscillate at a relatively low frequency (for example, 60 Hertz). The discharge lamps typically need a ballast circuit (for example, a magnetic ballast circuit) to interface with the power line. The ballast circuit for low frequency operation is generally bulky and operates the discharge lamps inefficiently.
Electronic ballast circuits have been introduced to increase power efficiency of the discharge lamps by converting the power line signal to a relatively higher frequency AC signal and driving the discharge lamps with the relatively higher frequency AC signal. The higher frequency AC signal requires less current to flow through the discharge lamps to achieve the same light output, and lower current flows can lengthen the life of the discharge lamps. Generally, electronic ballast circuits are much more expensive than magnetic ballast circuits.
Discharge lamps with filaments at opposite ends generally become inoperable when one or both filaments are worn out (or burned out). The burnt out discharge lamps are typically replaced with new discharge lamps. The burnt out discharge lamps need to be handled carefully because they may contain harmful elements, such as mercury. Improper handling during disposal of the discharge lamps can cause the mercury to inadvertently leak and contaminate the environment.